Experimental study on the flow conductivity of hydraulic fractures in different sedimentary rocks of tight oil reservoirs

Hydraulic fracturing is one important technology for the production increase and liquid level lifting of tight sandstone oil reservoirs, and evaluating the flow conductivity of hydraulic fractures accurately is the foundation of further productivity prediction. The uniform sanding mode is adopted in conventional laboratory experiments, but it cannot accurately simulate the gradual decline characteristics of proppant concentration in hydraulic fractures of actual reservoirs from the bottom hole to the distant end. To this end, this paper tested the flow conductivity of main fractures in the mode of nonuniform sanding by carrying out the flow conductivity testing experiment of multi-section nonuniform sanding on five types of sedimentary rock plates (beach bar sandstone, glutenite, turbidite and two types of outcrop cores). In addition, the reasons for the different flow conductivities of different sedimentary rocks were analyzed from the aspects of rock composition and size composition. The experimental results show that the average flow conductivity in the mode of nonuniform sanding is 4.7%~8.5% lower than that in the mode of uniform sanding. At the closure stress of 60 MPa, the lost flow conductivity of beach bar sandstone reservoir is the least, that of turbidite reservoir is moderate and that of glutenite reservoir is the largest, whose flow conductivity loss ratio is 38.9%~53.7%. That is because different sedimentary rocks are different in compression strength, which leads to different proppant embedment depths and consequently results in different flow conductivities. The research results provide a basis for maintaining the reasonable reservoir pressure of different types of tight reservoirs.